1. Field of the Invention
The present invention is related to a method for backing up a power supply of a disk array device and a system therefor.
2. Description of the Related Art
A disk array device has now come to be in use not only in a conventional machine room of stabilized condition but also in an ordinary office environment which may sometimes suffer continuing or instantaneous power failure and the like. In particular, as the disk array device is becoming more available through downsizing and employment of open architecture in CPU, the above situation is being spread. A typical configuration of power supply in a current disk array device is illustrated in FIG. 12 for example.
A disk controller 11 (DKU) of the disk array device 10 includes an error correction group 15 having a disk unit 13 comprising one or more disk drives 12, and a disk unit 14 for parity bits containing data recovery information for the disk unit 13. The disk unit 13 is referred to as a hard disk platter (HDD-PL) in FIG. 12, which is hereinafter simply referred to as a “platter.”
A DC-DC converter 16 is connected to the error correction group 15 including the plurality of platters to supply DC power output from an AC/DC converter 18 converting two systems of AC power 17 into DC power respectively. In this power supply system, a backup battery 19 is connected to the DC-DC converter 16. When either of the two AC systems fails, the backup battery 19 supplies power to the DC-DC converter 16 so as to allow the disk device to operate normally until AC power restoration.
According to nature of the disk array device, it is basic requirement to improve its availability. In this context, fault tolerance design has been introduced for hardware failure in the disk device. However, such design policy has not been fully applied to power supply for the disk array device. For example, in the above-mentioned conventional power supply system, failure of AC power is able to be backed-up by the batteries, but when the batteries themselves become inoperative due to such as failure, back up of power supply is not to be expected.
Performance of the back-up batteries is generally likely to be dependent on environmental factors such as temperature, vibration, and deterioration with time. Thus, it becomes impossible to provide sufficient power backup since the performance of the batteries is insufficient. One solution for the problem will be improvement in availability of the batteries by adopting full redundant system to the backup batteries. However, such redundant system will substantially increase initial and running costs and also cause a problem of where to equip the batteries.
Next, discussion will be given for each platter. As shown in FIG. 13, a disk array device which is also called a storage device or a disk subsystem, constituting a single platter typically comprises a disk controller and a disk drive. The disk controller receives request for data transfer from a host apparatus and perform data receiving and transmission. The disk drive including a hard disk drive (HDD) writes and reads data to/from the HDD under control of the disk controller. Additional drive is able to be provided if required to enlarge storage capacity of the disk array device.
Turning now to the disk controller, as shown in FIG. 13, the disk controller comprises a host interface control logic section, a cache memory, an interface control logic section of the HDD, power supply, and a power supply monitoring section. The host interface control logic section takes charge of interfacing between an upper or a host apparatus and perform processes such as accepting request for data transfer. The cache memory provides a temporary storage for data to be written in the disk drive which has been transferred from the host apparatus. The interface control logic section provides an interface with respect to data receiving/transmission between the HDD, i.e., writing/reading of the data to/from the HDD. The power supply generates predetermined DC output from AC input AC1 independently prepared for the disk controller, and supplies operating power to the host interface control logic section, a cache memory, and an interface control logic section of the HDD. See Japanese Patent Application Laid-open Publication No. Sho62-202228, Symbol 40 in FIG. 1, for example. The power supply monitoring section monitors conditions of external AC input and DC output from the power supply and reports the results of the monitoring to the host interface control logic section and the interface control logic section of the HDD.
Next, the disk drive will be described. As shown in FIG. 13, each disk drive comprises an interface control logic section of the HDD, an HDD and a power supply. The interface control logic section of the HDD transmits/receives data to/from the interface control logic section of the HDD at the disk controller side, and the HDD. The power supply generates predetermined DC output from AC inputs AC2 and/or AC3 independently prepared for each disk drive, and supplies operating power to the HDD and an interface control logic section of the HDD. See Japanese Patent Application Laid-open Publication No. Sho62-202228, Symbol 20 in FIG. 1, for example.
In the conventional example shown in FIG. 13, an uninterruptible power supply, hereinafter referred to as “UPS” is connected to each of the AC inputs AC1 to AC3. If the AC input is normally supplied, each UPS supplies the AC power as received to the power supply of the disk controller or the disk drive. If the AC input fails, each UPS supplies operating power from an auxiliary power supply for backup such as secondary batteries to various sections. For example, when a UPS for the disk controller detects an abnormal condition such as power failure continuing beyond one minute and determines that power is lost, the UPS reports the event to the power monitoring section of the disk controller. The interface control logic section of the HDD which was notified of the power failure by the power monitoring section controls so that the data temporarily stored in the cache memory is written into the HDD of the disk drive, thereby the data is secured when the AC input is lost. This procedure is typically called a destaging.
In the conventional example in FIG. 13, each disk drive is not provided with the power monitoring section. Therefore, a problem will arise when power failure occurs only in the disk drive but not in the disk controller.
One example of the problem is that even if power failure occurred at a certain disk drive, the disk controller is unable to detect the failure since the disk controller is unable to monitor the power condition of the disk drive.
More specifically, when data to be written into the disk drive with power failure is transferred to the disk controller from a host apparatus, the disk controller continues to accept the transferred data to be written since the disk controller is unable to monitor the power condition of the disk drive. The data to be written transferred from the host apparatus is temporarily stored in the cache memory and then transferred to the disk drive which is operating by means of auxiliary power from such as backup batteries. A problem is that the disk controller unable to detect power failure continues to transfer data to the disk drive which is operating on auxiliary power of limited capacity.
Furthermore, considering possibility of continuing data transfer, it is difficult to properly estimate the required capacity for auxiliary power supply. One approach is that time range required for power recovery is estimated first and capacity of auxiliary power supply is determined when maximum time required until the power recovery is assumed. As a result, the dimension for an auxiliary power supply must be maximum for maximum power capacity. On the other hand, if it is of higher priority to make a disk array device as a whole smaller, power capacity must be set minimum for a auxiliary power supply of, minimum dimension. In this case, it is necessary to assume minimum recovery time from power failure. In either case, it is hard to obtain proper capacity for a auxiliary power supply.